This invention relates to diaphragm pump apparatus, and particularly to a diaphragm pump apparatus wherein a mechanically driven piston provides a compressing force to a hydraulically driving fluid and this force is transmitted to a pumped liquid via a diaphragm assembly.
Prior art diaphragm pumps have had to solve the problem of controlling the hydraulic fluid supply to the chamber wherein the mechanical driving piston reciprocates, for the purpose of controlling the range of hydraulic fluid pressures which are developed. Since these hydraulic fluid pressures are transmitted to a diaphragm membrane which is typically of flexible and rather delicate construction, pumps of this type must be designed to guard against pressure imbalance across the diaphragm membrane. When fluid pressure imbalance across the diaphragm exceeds only a few pounds per square inch (p.s.i.) there is a danger that the diaphragm will rupture, resulting in a failure of the pumping mechanism. Further, since a great advantage of a diaphragm pump is that it enables complete isolation of the pumped fluid from the pumping chamber and mechanical parts of the pump, diaphragm rupture results in contamination of the pumped fluid with hydraulic pumping fluid or oil. Thus, not only will a diaphragm pressure imbalance result in a failure of the pumping apparatus, but also it will result in the contamination of the fluid being pumped and the internal parts of the pump itself.
There are two situations in which control over the pumping fluid pressure must be made. The first of these situations occurs when the fluid being pumped becomes pressure blocked and causes the reciprocating piston to work against excess pressure on the hydraulic fluid side of the diaphragm. In this situation the hydraulic fluid chamber must provide a relief means for bleeding off hydraulic fluid during the reciprocating piston compression stroke. The second situation occurs because of leakage from the hydraulic fluid chamber due to normal clearances, etc., and requires that hydraulic fluid be replenished into the chamber in order to maintain a sufficient quantity of hydraulic fluid for pumping to occur. The situation is typically handled by providing some sort of valving mechanism between a hydraulic fluid reservoir and the pumping chamber so that hydraulic fluid may be fed into the pumping chamber, either during the suction stroke of the reciprocating piston or whenever a predetermined negative pressure differential exists between the reservoir and the pumping chamber.
Prior art diaphragm pumps have solved the problem of relieving excess hydraulic fluid pressure under blocked pressure conditions of the pumped fluid by means of various valving mechanisms. Included among these have been spring-biased ball check valves, poppet valve assemblies, reed valves and other pressure-operated valves which unload the hydraulic fluid chamber under predetermined pressure conditions. The problem of replenishing hydraulic fluid into the pumping chamber has been solved by prior art devices using similar pressure relief mechanisms, some of which have been dependent upon piston stroke position of the mechanical driving apparatus. The present invention solves the problem of controlling hydraulic fluid chamber pressure in a new and novel way which is not found in the prior art.